The clay at Des Moines, Iowa, is very similar to the Sioux City clay in this : that it possesses quite a per cent. of sand and fire-clay. We do not wish to convey the idea that the sand and fire-clay are mixed or in the same vein, for they are not, either at Des Moines or Sioux City ; but at both places the clay bank is very high, having a working face of from fifty to one hundred feet, and in both the sand, clay and semi-fire-clay lie in pockets and different layers.
The Des Moines clay is more plastic in the natural state than any other similar clays ; in fact, it is found almost soft in portions of the bank, while in other portions it is quite hard and dense. This clay also requires a very high degree of heat, and stands up well in the kiln, and produces among the best paving-brick in the market. • Before passing, we would say that neither the Des Moines nor the Sioux City clays polish in the green state so readily to a smooth surface, and when burned do not break with quite so smooth or gloosy a fracture as some other clays.
At Middleport, Ohio, Garrett & McManigal are manufactur ing excellent paving-brick from a deposit made at some time, no doubt, by the Ohio river. This clay is plastic in the bank, has no resemblance whatever to soapstone or shale, is taken out of a flat field near the surface. It has very little sand. When soaked, becomes sticky and tough to the touch, shrinks considerably in burning, but stands up well under fire. Most brick-men would pronounce this a number one red brick clay ; in fact, the company was largely engaged in making dry pressed brick before going into the paving-brick business.
At Westerville, Ohio, Mr. J. W. Emerald is making paving brick from a clay which in appearance seems to be nothing more or less than a surface clay. We do not mean soil. The clay is very dark, almost black. It is very plastic and can be
handled easily with the spade, almost free from sand. This is a remarkable clay, one that few would ever suspect as suitable for paving-brick, but teaches that paving-brick material can be found in the swamps and marshes as well as in the hills and bluffs.
The above descriptions are intended to aid to some extent in the identificatiOn of paving-brick clays from their physical appearance.
The Cambria Iron Company, of Johnstown, Pa., has dis covered that the shale which is taken from its ore mines will make a superior quality of vitrified street paving-brick. The shale taken from the ore mines and dumped over the bank was thought to be entirely worthless until this discovery was made. Hundreds of thousands of tons of this shale are lying within several miles of Johnstown.
The Grape Creek Clay Company, Grape Creek, Ill., in the manufacture of its street paving-blocks, uses a shale clay which is found overlaying its coal measures at a depth of 120 feet and i6o feet respectively.
The clay on leaving the mines is more like rock than clay.
Shale alone makes a good paving-brick and will never wear out by attrition. Fire-clay alone, as usually worked, possesses a grainy nature ; when put in the pavement, will not sustain the amount of traffic without wear that is desirable.
The London Clay Company, of London Mills, Ill., make paving-brick of shale and potter's clay in such proportions as to get good results. The potter's clay, withstanding a high temperature, allows great latitude in the burning without mak ing the brick unshapely by melting or twisting ; while the shale, being less refractory, melts and forms a union of all the mass, yet being relieved of their glossy nature, making them tough, and capable of resisting the action of frost, and maintaining a smooth surface in the pavement.